A polycarbonate resin is excellent in mechanical strength, electrical characteristics, transparency, and the like, and hence has been widely utilized as an engineering plastic in various fields, such as the field of electrical and electronic equipment, and the field of automobiles. And also, the polycarbonate resin is utilized in a casing for a cellular phone, a mobile personal computer, a digital camera, a video camera, an electric tool, or the like. In these applications, impact resistance is important because of a possibility of dropping during handling in these application. In addition, a design property (especially a color) is also an important factor.
A resin material can be relatively easily colored and a colorful resin material has been used in many everyday things. In particular, a resin material having, for example, a white or gray color is frequently used. Meanwhile, a polycarbonate-polyorganosiloxane copolymer (hereinafter sometimes referred to as “PC-POS”) obtained by copolymerizing a polyorganosiloxane has been known. The PC-POS has been expected to find use in the above applications because the PC-POS is excellent in properties, such as impact resistance. Titanium oxide is desirably used as a pigment in the applications because while impact resistance is important, a design property is also important.
A composition obtained by combining a PC-POS and titanium oxide, the composition having a white external appearance and a satisfactory impact strength, has been known. For example, a polycarbonate-based resin composition that is excellent in mechanical properties, such as impact resistance and rigidity, optical characteristics, and the like, and that is also excellent in reflectance characteristic (see Patent Document 1) has been known. According to Patent Document 1, a PC-POS-containing composition whose titanium oxide content has been set to 5 to 10% shows a satisfactory reflectance and a satisfactory mechanical strength. In another example, a polycarbonate-based resin composition that shows excellent flame retardancy without a phosphorus-based flame retardant nor a halogen-based flame retardant, that has high reflectivity and a high light-shielding property, and that is excellent in thermal stability has been known (see Patent Document 2). According to Patent Document 2, a PC-POS-containing composition whose titanium oxide content has been set to 5 to 50% shows a satisfactory reflectance, a satisfactory Izod impact strength, and satisfactory flame retardancy.
The compositions disclosed in those Documents show high light-reflecting characteristics, but meanwhile, their strengths are lower than a strength inherent in a PC-POS because their titanium oxide contents are large. In addition, in the above applications, the specific gravities of the compositions were larger than a proper value. Accordingly, the development of a PC-POS-containing composition reduced in titanium oxide content while having a satisfactory reflectance, a satisfactory mechanical strength, and the like has been desired.
A composition containing a relatively small amount (e.g., 1 to 2.5 wt %) of titanium oxide and a PC-POS has also been known (see Patent Document 3).
In the PC-POS-containing composition disclosed in Patent Document 3, titanium oxide has been used in a small amount as means for improving its flame retardancy. In this Document, however, there is no disclosure concerning its color appearance.
In Patent Document 4, there is a disclosure of a polycarbonate-based resin composition excellent in appearance and impact resistance of a molded product as a result of the use of a PC-POS whose polyorganosiloxane (hereinafter sometimes referred to as “POS”) moiety has a short chain length and a PC-POS whose POS moiety has a long chain length. In Patent Document 4, a polycarbonate-based resin composition that is free of the occurrence of a black streak or the like and is hence excellent in surface appearance can be obtained, but a problem in that its impact resistance, in particular its impact resistance at low temperature is not sufficient occurs.